Geoscience Reference
In-Depth Information
[5,133,134]
. Both iron oxide and cobalt oxide nanoparticles were obtained via the
following reactions:
2Fe
ð
NO
3
Þ
3
1
3H
2
O
Fe
2
O
3
1
6HNO
3
5
6Co
ð
NO
3
Þ
2
1
12NaOH
O
2
5
2Co
3
O
4
1
12NaNO
3
1
6H
2
O
1
The effect of operating parameters such as experimental temperature, feed concen-
tration, residence time, and salt:sodium hydroxide ratio on particle size, size
distribution, and morphology have been examined for these materials. Also thermody-
namic modeling has been carried out on these systems to understand the relationship
between particle morphology and species distribution
[134]
. However, most of these
works yielded the nanoparticles which were not well dispersed because of the coagula-
tion factor with the size reduction. In order to overcome that problem, several
researchers have tried to use the surfactants route to synthesize nanoparticles of very
high quality with smaller particle size and highly dispersed under SCF conditions
[135,136]
. Use of surfactants does not alter the crystal structure, but greatly alters the
surface morphology and surface charge of nanoparticles, by controlling the nucleation
and crystal growth. Several modifiers like decanoic acid, oleic acid, and hexaldehyde
have been used.
Figure 10.30
shows the cobalt oxide nanoparticles synthesized by
Adschiri and coworkers with and without surface modifiers. The size of the particles
can be very effectively controlled by appropriately maintaining the molar ratio of the
modifier to starting material and the type of surfactant.
Figure.10.31
shows the size
control for Co
3
O
4
nanoparticle fabrication under SCF conditions.
There are several reports dealing with the deposition of magnetic nanoparticles on
activated carbon, HAp, porous media, and several other templates
[133]
.However,the
fabrication of magnetite nanoparticles in conjugation with several biodegradable poly-
mers and coatings using the SCF technology is still a developing field.
Perrotta
[136]
, Laudise and Ballman (1958) [137], and Al'myasheva et al.
[138]
have reviewed the hydrothermal synthesis of corundum nanoparticles under hydro-
thermal conditions. A high specific surface area corundum has been synthesized
Figure10.30 TEM images of Co
3
O
4
nanoparticles prepared using SCF technology: (a)
without surface modifier and (b) with surface modifier C
9
COOH at 300
C and 20 MPa
Source: Photographs courtesy Prof. T. Adschiri, Tohoku University, Jaan.
